I don't think the problem comes from the system itself but from some choice made.
Most job currently have a big disparity between good choice, useless choice and mandatory leaving most job with very little choice.
There is basically either too not enough good choice, or (specifically for healers), too many things are just a no brainer living no room foor customization.
Tank have probably the best choice so far since the only skill they actually need (on most fight at least), is Provoke for tank swap.
But then, when we look at the gain some skill are clear winner over others. Too many skill are just too situationnal to be concidered"good" out of a specific fight (Like Awareness and Interject for OS3 for instance).
So once we remove the niche fight. We end up with the same 5 skills on most tanks.
Provoke, Rampart, Convaslescence, Reprisal, Shirk/something else.
Same goes for healers.
LucidDream and Protect are just too good to not be taken, Swiftcast is somewhat mandatory if you want to be able to rez and of course Esuna for the few fight that require it.
Then you have the "always good" Largesse.
Once that done you're left with actually very little choice. E4E is too random and will only work well on a few fight. Surecast is very situational (which is fine), Rescue could be cool if the person you'd pull in wouldn't always die because of the delay.
Then there is break which is always useless (even in Solo) and Cleric Stance which is just... lame.
DPS somewhat suffer the same issue than Tank, there are only 5/6 good choice, which in the end means there's no proper choice.
In order to make this system the way it was intended,
first they need to make all truly mandatory skills baseline (notably Provoke, Esuna. Although it's not absolutely mandatory I'd add lucid dream)
Then, they need to make new skills or somewhat rework currently existing skill in a way that doesn't force the player to get a specific skill.
For instance, Swiftcast is notably taken to get instant rez (spare BLM). Assuming there would be other interesting choices, if they'd make rez instant (they could add a 1min CD to the skill to compensate i dunno), then Swiftcast would loose a lot of its appeal.
There is a limited amount of things you can do in term of situational skills.
For instance, anything that could substantially increase a dps' dps can't really be added because it would make the skill mandatory, and as far as i'm concerned, the point of this system to give you some choice and way to personalise.
Another thing that could be done would be to instead of adding skills, adding traits.
For instance
These spells are now baseline: Esuna, Protect, Lucid Dream
Healer
Improved Ressurection - [Skill] : Ressurect a dead player (no weakened state), 360sec, instant, 3600mana
Swift Resurection - [Trait] : Ressurection cast time is reduced to 3sec.
Cleric Stance: - [Skill] Increase damage by 5% and reduce damaging spell mana cost by 50%, last 15sec, 90sec CD
Improved Lucid Dream - [Trait] : Lucid Dream cooldown is reset upon death.
Eye for an Eye - [Skill] :Increase healing received proportionally to the missing health. Up to 100%. Last 10sec. 90sec CD
hp - heal bonus
100% - 0%
75% - 25%
50% - 50%
25% - 75%
1% - 100% (gl there)
Justification:
These proposition are highly situational and most importantly, group/player dependant.
Improved Resurection is nice in farm group or when you're close to down a boss.
If you're learning a boss and people overall keep dying, then it is not a really good skill. Perhaps Swift resurection would be better.
Then again, Swift resurection would be a non interesting skill if your party, overall, has no one dying. (like any farm group should)
Improved Lucid Dream is again, a very nice skill for progression if you keep dying because you're struggling with the fight. It's a rather bad trait if you simply never die.
The mana cost reduction on cleric stance is to make the talent more interesting. Honestly, 5% dps increase is hardly worth it. At least with the mana cost reduction it can be used for high AoE moment. This could be a rather interesting choice for dungeons.
E4E could be more reliable.Most fight have hard tank buster, this could be a useful spell to help bringing back a tank up. There are quite a few fight where increase the healing done by an ogcd would be very nice.
Most are highly " progression oriented ", but this is pretty much my point, by giving more good choice that are not simply fight dependant but also skill / group dependant, you could see more variation.
I don't think it is possible to make 10-15skills perfectly balanced and good in all situation. However I do believe making skill optimised for specific tast / moment could work fine.
Tank
Swift Stance [Trait] - Stance are now out of the GCD but get a 15sec CD.
Ultimate Sacrifice [Skill] - Heal the target for up to 50% of your maximum HP. Reduce your HP by half of the healing done. Instant. 120sec
Improved Provoke - [Trait] - Provoke also generate half your health as enmity to the target.
Last Stand - [Skill] - You defy death. You automatically resurrect after 5sec in a weakened state with half your maximum health. 10sec duration. 600sec recast
Justification: Again mostly progression skills. Yet again, some group / player could hihgly benefit from these skills instead of the current one. Ultimate sacrifice could ease a tank buster, or perhaps your healer died and the MT is getting low?
Caster
Drain [Skill] - Potency 100 - Same as before except that the heal can heal around 30% of your maximum health. Instant - 30sec recast
[B]Etherical Come back - [Trait] - Reduce the duration of Weakened State by 1min and reset all your skill upon death. 600sec CD
I don't have much idea for the melee and range.
But you get the idea.